Jay Z and Danger Mouse - What more can I say (the gray album)
Georgia by Ludacris (orig. Georgia on my mind by Ray Charles)
San Francisco Knights by people under the stairs
Acid Raindrops by People under the stairs

Canto de Ossanha by Jurassic 5 (well just their DJ's Cut Chemist and Nu-mark). AWESOME track! prob listened to it a 100 times! if you listen to the original (same title by Baden Powel) you'll see why it's so cool - they use pretty much every part of the original song, but they mash it up to make it more hip hop'y and it just sounds great.

lastly, one of my favorites, just because the intro is so cool, "thin line" by Cut Chemist feat Jurassic 5 and Nelly Furtado. he starts off with the whole classic track, then breaks it down to just the original song's bass line. definitley worth a listen.